Peru meteorite may rewrite rule books

Wednesday, 12 March 2008 Maggie FoxReuters

The meteorite that caused this 15 metre crater in Peru last year should have disintegrated in the atmosphere long before reaching earth. But it kept going, travelling 40-50 times faster than expected (Source: Reuters/Miguel Carrasco/La Razon )

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A meteorite that struck Peru in September, digging out a deep hole and startling nearby residents, behaved so strangely that scientists may have to rethink what happens when space objects hit planets.

The rocky meteorite travelled faster and hit harder than the US researchers expected.

The object, which left a 15 metre crater, theoretically should have disintegrated in the atmosphere long before reaching the earth's surface, says Peter Schultz, a professor of geological sciences at Brown University.

And it may have. But the pieces stayed together and were speeding at 24,000 kilometres per hour when they hit, Schultz told the Lunar and Planetary Science Conference in League City, Texas.

Usually only meteorites made of metal make it to the surface intact enough to scoop out a crater.

"They come into the atmosphere, they slow down, and they plop," Schultz says.

"It would make a hole in the ground, like a pit, but not a crater. But this meteorite kept on going at a speed about 40-50 times faster than it should have been going."

It landed in an arroyo, or dry stream, and the pit quickly filled with water from underneath the surface.

Schultz says his team's observations suggest that scientists may need to change theories about the different ways objects can hit planets.

"We have to go back to the drawing board and think again," he says.

Separating fact from fiction

Dozens of people who visited the crater, near Lake Titicaca and the border with Bolivia, reported vomiting and headaches afterward. Some questioned whether the noise and hole were actually caused by a meteorite.

"That is one of the reasons we went down. We wanted to distinguish fact from fiction," Schultz says.

"These reports of all these people being sick were grossly exaggerated. They didn't get sick. They were surprised."

A team from the NASA Johnson Space Center in Houston analysed two chunks of dark grey rock from the meteorite and told the meeting they look nothing like meteorites from known sources such as Mars.

Schultz, whose team inspected the crater 1300 kilometres south of Lima, says its unusually loud and messy impact happened because it was spinning and going so quickly.

"This just isn't what we expected," Schultz says. "It was to the point that many thought this was fake. It was completely inconsistent with our understanding of how stony meteorites act."

Survivor

At such high velocity, fragments may not escape past the 'shock wave' barrier accompanying the meteorite, he says.

"It became very streamlined and so it penetrated the earth's atmosphere more efficiently," Schultz says.

He compares it to a flock of geese flying behind one another in a 'v' shape.

He says this could challenge conventional wisdom that all small, stony meteorites disintegrate before striking earth.

"You just wonder how many other lakes and ponds were created by a stony meteorite," says Schultz. "But we just don't know about them because when these things hit the surface they just completely pulverise and then they weather."

The findings may also help explain what caused various craters on Mars, he says.